1. Field of the Invention
The present invention relates to an engine controller for carrying out throttle control at a high speed with a pinpoint accuracy using a throttle actuator, and more specifically, to an engine controller for improving a substantial throttle control resolving power using a less expensive A/D converter having a low resolving power without particularly using an expensive A/D converter having a high resolving power.
2. Description of the Related Art
Conventionally, a throttle valve acting as an output regulating restricter is mechanically associated with an accelerator in ordinary automobile engines and the degree of opening of the throttle valve is controlled by linking it with the accelerator through a wire or the like.
On the other hand, recently, attention is paid to electronic throttle actuators for driving a throttle valve by a motor. Devices using the throttle actuator detect an amount of depression of an accelerator pedal (degree of accelerator opening) as an electric signal by a degree of accelerator opening sensor, determine a target degree of throttle opening from the degree of accelerator opening through predetermined calculation and supply a control amount corresponding to the target degree of throttle opening to the throttle actuator to thereby control the opening/closing of the throttle valve.
Since this type of the electronic throttle actuators can realize a high engine control capability as well as improve the safety of automobiles, they are used to automobile traction control, constant speed traveling control, idle speed control (generally, referred to as ISC) and so on.
For example, the ISC (idle speed control) which is typical in engine control is disclosed in Japanese Unexamined Patent Publication No. 63-49112. In this case, an idle rotation speed is controlled to a predetermined speed in accordance with a water temperature and an electric load by regulating an amount of air flowing through a bypass.
That is, the apparatus disclosed in the publication disposes the bypass which bypasses a throttle valve to a throttle chamber and regulates the area of the bypass by an actuator to thereby regulate the amount of air flowing through the bypass. The apparatus also realizes a first idle function by disposing an air regulator to the bypass.
However, a cost is increased in this type of the apparatus because auxiliary devices such as the bypass, its flow amount control means and so on are required.
To cope with the above problem, there is proposed a method of realizing the ISC and first idle control functions by improving a control resolving power in idle operation as disclosed in, for example, Japanese Unexamined Patent Publication No. 6-101550.
The apparatus disclosed in the publication feeds back a degree of throttle opening by comparing it with a target degree of throttle opening by amplifying the gain of a degree of throttle opening sensor in the low opening region thereof which detects the degree of opening of a throttle actuator.
Conventionally, when the ISC is carried out using the electronic throttle actuator, since it is required to control an engine speed with a pinpoint accuracy, a resolving power in the control of the degree of throttle opening is a problem. This is because that since the throttle valve is designed to cause an automobile engine to generate a maximum output when it is entirely opened (a passage area is maximized), a control amount corresponding to a maximum flow amount when the throttle valve is entirely opened must be calculated as well as a control amount corresponding to a fine degree of throttle opening must be also calculated when a small amount of air flow is controlled in the ISC.
Therefore, the ISC having a pinpoint accuracy can be realized by the throttle actuator based on a control amount calculated by amplifying the gain of a signal detected by the degree of throttle opening sensor in a low opening region and improving a calculation control accuracy in a region where an amount of air flow is small in the ISC.
In this case, however, since the throttle control accuracy is improved using the degree of throttle opening sensor which has the high gain only in the SIC region as described above, the high accuracy region is narrow and a special electronic device must be added to amplify the gain, by which a cost is also increased a circuit is made complex.
Further, recently, although a high accuracy is required not only in the region where an amount of air flow is small but also in an entire region as the use of the throttle actuator, controllability in the region where an amount of air flow is large cannot be improved in, for example, the traction control, the constant speed control and the like.
As described above, conventional engine controllers have a problem that a cost is increased because the apparatus disclosed in, for example, Japanese Unexamined Patent Publication No. 63-49112 must be provided with the bypass, the flow control means thereof and the like across the throttle valve.
Further, the apparatus disclosed, for example, Japanese Unexamined Patent Publication No. 6-101550 also has a problem that a cost is also increased because the circuit device for amplifying the low level signal from the degree of throttle opening sensor to realize the control and calculation of the high resolving power in the region where the degree of throttle opening is small.
An object of the present invention made to solve the above problems is to provide a high speed engine controller having a pinpoint accuracy at a low cost without using an expensive A/D converter having a high resolving power in the control of a throttle actuator which does not use a bypass.